Biomedical Engineering Reference
In-Depth Information
11 Innovative systems and applications
Our
final chapter is intended to serve as a guide not only to novel systems but also to
recent and potential future applications. The majority of exciting developments are in the
pharmaceutical and biomedical areas, including scaffolds for tissue engineering, so
biomedical applications make up, by some way, the largest section here. Moreover, for
practical reasons this chapter is shorter than we might wish and covers only a limited
selection of topics. We apologize in advance if this does not give appropriate weight to all
relevant developments.
11.1
Innovative systems
11.1.1
Slide-ring gels
Perhaps the most intriguing of recent novel physical gel systems are the so-called
slide-ring gels pioneered by Ito and co-workers (Okumura and Ito,
2001
; Ito,
2007
,
'
cross-linked
'-
actually topologically interlocked
-
by a supramolecular closed
shaped molecule. Each polymer chain
threads through one of the two loops and can translate freely, but is always held adjacent
to the other chain by the
figure-of-eight
-
rst proposed
by de Gennes (
1999
), but only subsequently has supramolecular chemistry helped to
realize the concept. As the cross-links can pass along the polymer chains freely,
equalizing the tension of the threading polymer chains like a system of pulleys, their
behaviour has been called the
figure-of-eight (
Figure 11.1
). Such a structure was
'
pulley effect
'
. The chemistry of synthesis is obviously
testing, but
first produces a polyrotaxane (PR). A rotaxane is a supramolecular structure
consisting of one or more ring-shaped cyclic molecules and a linear molecule threaded
through the rings and
at both ends, forming a dumbell shape so that the ring can
move along the molecular axis but no further. If the linear molecule is polymerized it
should give a necklace-like chain onto which cyclic molecules can be threaded.
In the work by Ito and co-workers, the polyrotaxane contained a small amount of an
'
capped
'
α
-CD) on poly(ethylene glycol) (PEG). The slide-ring gel was then
prepared by cross-linking
-cyclodextrin ring (
α
α
-CDs on different PR chains, though not all
α
-CD rings were
so linked to give
-CDs cannot diffuse
off of them. Although the precursor system was prepared in 2001 (Okumura and Ito,
figures-of-eight. Since the chains are capped, the
α
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